Write the growth formula in an R script. Define initial par values. Input the size and age data. Plot the size and age data as points. Plot the growth model with the initial par values as a line. Play with the initial par values until you see a good agreement between the model (the line) and the data (the points). Optimise. Re-plot. Plot a residual histogram. Plot a residual scatterplot. Plot a Q-Q residual plot.
HTH Rubén ____________________________________________________________________________________ Dr. Rubén Roa-Ureta AZTI - Tecnalia / Marine Research Unit Txatxarramendi Ugartea z/g 48395 Sukarrieta (Bizkaia) SPAIN > -----Mensaje original----- > De: r-help-boun...@r-project.org > [mailto:r-help-boun...@r-project.org] En nombre de Renalda > Enviado el: sábado, 04 de junio de 2011 6:17 > Para: r-help@r-project.org > Asunto: [R] logistic growth model > > I want to Fit a logistic growth model for y = k > *eb0+b1(age)/1 + eb0+b1(age), can some one help on how to get > the initial coefficients b0 and b1? I need to estimate in > order to do the regression analysis. When I run using b0=0.5 > and b1=3.4818, I get the following error > > 397443.8 : 0.5 3.4818 > Error in nls(Height ~ k * exp(b1 + b2 * Age)/(1 + exp(b1 + b2 > * Age)), : > singular gradient > "please tell me what is wrong with my initials values, and > how to get the initial values" > > ______________________________________________ > R-help@r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide > http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code. > ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
